1. Technical Field
This invention relates to the use of a molecular marker, BC200 RNA, in screening for neoplastic diseases. Methods may be used by which BC200 RNA expression may be monitored and utilized for both the diagnosis and prognosis of carcinomas.
2. Background of Related Art
Progress in the diagnosis and prognosis of cancer has been hampered by the lack of suitable, reliable and sensitive molecular markers. Such indicators are necessary to identify lesions and characterize them, to distinguish benign from malignant tumors, and to be able to determine whether a given non-invasive carcinoma will become invasive in the future.
For example, no reliable molecular marker is currently available that could be used to complement mammography in the detection of breast cancer. This contrasts with prostate cancer, for example, where prostate-specific antigen (PSA) status can be established by simply analyzing a blood sample. PSA is a molecular marker for prostate cancer (reviewed by Gamick et al., “Combating Prostate Cancer”, Sci. Am. 279:75-83 (1998)), and although PSA status is not a very reliable tumor indicator (with relatively high false negative and false positive rates), it is routinely used in the clinical diagnosis of prostate malignancies.
Other markers for tumors are also known. For example, carcinoembryonic antigen (CEA) is of prognostic value for colorectal carcinoma; in breast cancer, CEA and CA15-3 are used as postoperative markers (Mughal et al., “Serial Plasma Carcinoembryonic Antigen Measurements During Treatment of Metastatic Breast Cancer”, JAMA 249:1881-1886 (1983)), but not in preoperative diagnosis. BRCA1/2 status can be used as a risk factor indicator, HER-2/neu (c-erbB-2) status correlates with relapse and survival (Slamon et al., “Human Breast Cancer: Correlation of Relapse and Survival With Amplification of the HER-2/neu Oncogene”, Science 235:177-182 (1987)), and Ki-67 is a proliferation marker that is useful in the determination of the growth fraction of a tumor (Gerdes, “Ki-67 and Other Proliferation Markers Useful for Immunohistological Diagnostic and Prognostic Evaluations in Human Malignancies”, Semin. Cancer Biol. 1:199-206 (1990)). However, these markers are of limited usefulness in tumor detection, diagnosis and prognosis.
BC200 RNA is a 200-nucleotide long, non-translatable RNA that is prevalently expressed in the nervous system of primates, including man. A partial nucleotide sequence of BC200 RNA from monkey brains was first reported by Watson and Sutcliffe, Molecular & Cellular Biology 7,3324-3327 (1987). This 138 nucleotide sequence showed substantial homology to the Alu left monomer, a sequence that is repeated many times throughout the human and other primate genomes. The sequence of full-length BC200 RNA was subsequently reported by Tiedge et al., “Primary Structure, Neural-Specific Expression, and Dendritic Location of Human BC200 RNA”, J. Neurosci. 13, 2382-2390 (1993).
The primary sequence of human BC200 RNA is as follows:
[SEQ ID NO 1] XXCCGGGCGCGGUGGCUCACGCCUGUAAUCCCAGCUCUCAGGGA GGCUAAGAGGCGGGAGGAUAGCUUGAGCCCAGGAGUUCGAGACC UGCCUGGGCAAUAUAGCGAGACCCCGUUCUCCAGAAAAAGGAAA AAAAAAACAAAAGACAAAAAAAAAAUAAGCGUAACUUCCCUCAA AGCAACAACCCCCCCCCCCCUUU
Expression of the small neuronal non-coding transcript BC200 RNA, itself a modulator of translation (Wang, et al., “Dendritic BC1 RNA: Functional Role in Regulation of Translation Initiation”, J. Neurosci, vol. 22, pages 10232-10241(2002)), is tightly regulated. The RNA is not normally detected at higher than background levels in non-neuronal somatic cells (Tiedge et al., supra). However, the tight neuron-specific control of BC200 RNA expression is deregulated in various tumors, including breast tumors. BC200 RNA is associated with malignancy and is not detectable in normal non-neuronal somatic tissue or in benign tumors such as fibroadenomas of the breast. Lin et al. “Expression of Neural BC200 RNA in Breast Cancer”, Era of Hope Proceedings, Vol. 1, p. 122 (Department of Defense, 2000).
U.S. Pat. Nos. 5,670,318 and 5,736,329, the contents of each of which are incorporated by reference herein, disclose the complete sequence of human BC200 RNA and the use of polynucleotide probes which can be used to specifically detect the presence of human BC200 RNA in a tissue sample.
The primary sequence of BC200 RNA can be subdivided into three structural domains. Domain I is nucleotides 1-122 and is substantially homologous to Alu repetitive elements which are found in high copy numbers in primate genomes. However, this region includes two bases not found in Alu or SRP-RNA, i.e., nucleotides at positions 48 and 49, which can be used to develop amplification primers specific to BC200 RNA sequences. Domain II is an A-rich region consisting of nucleotides 123-158. Domain III, consisting of nucleotides 159-200, contains a unique sequence with no homology to other known human sequences which can be used to identify BC200 RNA in tissues.
Oncological pathologists have long recognized that the differing degrees of malignancy of tumors is reflected in their morphological structure. There are three general grades of tumors, low, intermediate and high, with the high grade typically being associated with the most aggressive tumors (Elston et al., The Breast, Ch. 17, pp. 365-383, (1998)).
Ductal carcinoma in situ (DCIS) is a common but heterogeneous group of neoplastic diseases. Approximately 25% of DCIS will develop into invasive carcinomas within 15 years if left untreated (Elston et al., The Breast, Ch. 14, pp. 249-281, (1998)). However, to date there is no reliable indicator, molecular or otherwise, to predict the invasive potential of a given DCIS. Most women therefore elect to have DCIS removed surgically, which in many instances is unnecessary and amounts to over-treatment (Ernster, “Increases in Ductal Carcinoma In Situ in Relation to Mammography: A Dilemma”, NIH Consensus Development Conference on Breast Cancer Screening for Women Ages 40-49, pp. 147-151 (NIH, 1997)).
Clearly, a reliable prognostic indicator of cancer, including DCIS, would be most valuable in assisting physicians and patients in making informed treatment decisions.